Biphenyltriphenoxysilane



nited S ates Pat BIPHEINYLTRIPHENOXYSILANE Herbert C. Kaufman, WestHaven, Conn., assignor to John B. Pierce Foundation, New York, N.Y., acorporation of New York No Drawing. Application March s, 1956 Serial No.569,249 2 Claims.v (Cl. 252-78) closes as a heat transfer mediummixtures of tetra aryl orthosilicates. Morgan et a1. U.S. Patent No.2,674,579 discloses mixture of certain phenyl aryloxy silanes preparedby the reaction of phenyl' trichlorosilane with a mixture of phenol andcresol. All of these compounds, however, suffer the disadvantage of lowresistance to decomposition upon being heated for long periods of time.Such decomposition is probablycaused by poly: merization and isevidenced byan increase in viscosity. Moreover, since the individualcompounds for the most part are solids, mixtures must be prepared inorder to i provide a fluid system.

An object of the invention is to produce a heat transfer medium that isa single liquid compound and hence is fluid without being a mixture.

Another object of the invention is to provide an improved heat transfermedium which is fluid at low temperatures and resistant to undesiredincrease in viscosity with time at high temperatures. Still anotherobject is to provide heat transfer liquids which have a viscosity below700 centistokes at room temperature, good thermal stability,- resistanceto hydrolytic attacl are non-corrosive to metals encountered in heattransfer systems, and possess desirable heat transfer properties andphysical constants. The product which fulfills the objects of theinvention is biphenyl triphenoxysilane, represented by the followingstructural formula:

The product of the invention includes compounds in which the position ofthe silicon atom on the aromatic nucleus is ortho, meta or para, ormixtures of any of them. The products withthe meta or para linkage arepreferred, solely for reasons of availability and convenience.

Whereas prior heat transfer media have been characterized by increasedviscosity when heated at elevated temperatures of 700 to 800 R, anoutstanding, unexpected and advantageous property of the product of thisinvention is that its viscosity not only does not increase but actuallydecreases upon heating. The increase in viscosity found in the case ofprior compositions indicates that polymerization is the principalmechanism of thermal decomposition or degradation. For heat transferpurposes, such viscosity increase ultimately causes intolerable loss inheat transfer ability of the liquid, because viscosity is thedominantparameter of heat transfer and low viscosity is always'favorable. Any liquid which, through some anomaly, decreases itsviscosity whenheated improves rather impairs its heat transfer ability.g A

The improved heat transfer medium of the invention may be prepared asfollows: 1.2 moles, 346 grams, of a 50-50 mixture of meta and parabiphenyl-trichlorosilane,

(a commercially availablematerial) were melted at 45 C. and addedrapidly to 4.3 moles, 406 grams of melted phenol at 45 C. with"stirring. The phenol was in excess by 0.7 mole or 68 grams to insurecomplete reaction with the chlorosilane. HCl was evolved vigorously asheat was applied. The mixture was refluxed at 262C. for 20 hours, thencooled and stripped of excess phenol at reduced pressure.- grams ofphenol were recovered, as well as 515 grams ofbiphenyl-triphenoxysilane, representing a yield of 93.3% based onbiphenyltrichlorsilane. The properties of the product were as follows:

Color: Lemon, clear Boiling point: 438 C; (820 F.) at 764mm. HgKinematic viscosity (Fenske):

0 C. (32 F.)--3300 centistokes" 25 C. (77 F.)139 centistokes 370 C. (700F.)-0.474 centistoke The viscosity ofthe product may be in the range70.to 700 centistokes at 25 C.

The reaction will take place' merely. upon mixing of the compounds atroom temperature, but the temperature is selected to facilitate thecontrolof the, reaction. Since the-reaction proceeds in accordance withthe general rules of chemistry and is accelerated by heat, it ispreferred to heat the reactants to an eleva'ted temperature up to thereflux temperature of the reaction mixture at some stage during thereaction, preferably near the end, to hasten and assure its" completionand to remove the last traces of HC1. Alphysica'l scavenger (such as astream of inert gas) may 'be used'to facilitate the removal' of theby-product, hydrogen chloride; or ammonia or an organic base such'as'pyridine or tertiary amines, etc., that combine with the hydrogenchloride to give a non-corrosive by-product, may be used.

In performing the reaction, caution should be taken to prevent evolutionof hydrogen chloride gas at an excessive rate. This may be done byadding the phenyltrichlorosilane gradually to the phenol while themixture is at an elevated temperature. If desired, however, all of thereactants may be mixed initially, provided the tem perature is not aboveabout 45 C., and thereafter the temperature may be raised gradually.

In order to compare the stability of the product of the invention withother heat transfer media heretofore known, a product was prepared inaccordance with the Morgan Patent No. 2,674,579 as follows:

Into a reaction vessel equipped with an agitator and reflux condenserthere was placed a mixture of 1.8 moles of phenol and 1.2 moles ofcresol. The mixture was heated to 64 C., and 1.0 mol ofphenyltrichlorosilane (a commercially available product) was addedgradually over a period of one hour while maintaining the temperature ofthe reaction mixture at approximately 60 C. The reaction mixture wasthen heated gradually to reflux temperature and maintained there for aperiod of several hours to complete the reaction. The finished productlphenyl, phenoxy, cresoxy silane, 4:

was a mixture of the following compounds.

Ice PatentedFeb. 9, 1960 as an indication of thermal decomposition (orheat stability): The" resultsof" the-heatingtest' are shown -in* thefollowing table:

Kin.".viscosityr(25 O.) in centlstokes-heat tested at 700 F.

..'T'ime;'i(da'ys)u;--' -i-- 4 11 24 26 as Z 39 46 56 68 115 213 mnmiimmune; .165 1 125 100 r 84 s3 .r 83 7s 7s 76 Phenyl, Si Co)phenoxy(OCH;)1.:.eresoxy f,- l i 7 The viscosity of the phenylphenoxycresoxy silane in- Y -L creased markedly uponlheating, indicatingsubstantial 2 4 polymerization, whereas the viscosity of the product ofthe invention didgnotxincrease but in fact reflected a e decrease,indicating superior heat transfer properties. l Although specificembodiments of the invention have R v beendescribedherein, it isintended to cover, within the i 1 2o scope of theaappended claims allmodifications and (3) v r equivalents :within theispirit, and teachingof-the invention.

0 m I claim:v 4 y 1. Aacompound having: the following structural fori H2s' Oolor:-Yellow,.

Viscosity: 55 cs./77 F.

The products were both subjected to the following accelerated aging andstability test. A'sample ofeach liquid was placed'iii' a glass, tubeenclosed at the bottom andlhaving an openjj capillaryat the-top, open tothe atmosphere. Tlie tubes 'were immersed in a thermoiriwhich-theposition of the silicon atom'onthe aromatic vnucleus is of the groupconsisting of ortho, meta and para, and mixturesvof any of them.

2. The method of transferring heat to materials in indirect contactwitha heat transmitting medium, which comprises using, as a, heattransmitting medium the compound described in claim 1.

ReferencesnCit edin the file of this. patent UNITED STATES PATENTS2,584,334 Da Fano Feb; 5, 1952 2,626,266 Barr Ian. 20, 1953 2,674;579Morgan et a1 Apr. 6, 1954 2,701,803 -O'rkin Feb. 8, 1955 2,800,495

Haluska- July 23, 1957 UNITED STATES PATENT CERTIFICATE OF CORRECTIONPatent No. 2324, 574 February 9 1960 Herbert C. Kaufman It is herebycertified that error appears in the printed specification of the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

Column 2, line 419 for phenyltri--". read xenyltri- Signed and sealedthis 9th day of August 1960.

(SEAL) Attest:

KARL H, AXLINE ROBERT C. WATSON Attesting Officer Commissioner ofPatents

1. A COMPOUND HAVING THE FOLLOWING STRUCTRUAL FORMULA